Gas-filled rectifying tube



` ug. 29, 1950 Y M. KUlPERs 255207218 GAS FILLED RECTIFYING TUBE FiledJuly 2, 194e AGENT Patented ug. 2.9-, 1950 GAS-FILLED RECTIFYING TUBEMinne Kuipers, Eindhoven, Netherlands, assigner i to Hartford NationalBank and Trust Company, Hartford, Conn., as trustee Application July 2,1946, SerialNo. 680,891 In the Netherlands March 6, 1943 Section 1,Public Law 690. August 8, 1946 Patent expires March 6, 1963 5 Claims.(Cl. Z50-27.5)

This invention relates to gas filled rectifying tubes having two or moreanodes and wherein the incandescent cathode is disposed within a cathodescreen, more particularly a rectifying tube for high voltages i. e.several thousand volts.

Rectifying tubes having a plurality of anodes are often used since withthe same power they occupy less space than a corresponding number oftubes having one anode. Since, moreover, the feed transformer has asingle heating winding the construction of a rectifier equipped with arectifying tube having a plurality of anodes is particularly simple andcheap. One advantage of a tube having a plurality of anodes with respectto the tube having one anode and the same power is that the alternatingvoltage superposed on the rectified voltage is smaller and in additionthat the load conditions for the cathode are more favourable, since theratio of the maximum current to the average current is smaller.

One drawback of tubes having a plurality of anodes consists in thatthere often occurs arcing back in one discharge path or a directbreakdow-n between the two anodes and in addition th-at the anodes areliable to strong disintegration, due to which the tubes soon blacken andbecome unserviceable. With tubes having one anode substantially no ionsare formed in the negative phase, so that practically only the ionsavailable by the end of the positive phase find their way to the anode.In tubes having a plurality of anodes, however, ions are being steadilyformed in the discharge paths in the positive phase. These ions gain atleast partly access to the discharge paths of the negative phase whichinvolves a stronger bombardment by ions and this brings about theaforesaid drawbacks of arcing back, breakdown and blackening of thetubes.

To avoid the aforesaid drawbacks in tubes having two or three anodes ithas already come to be known to place one or more screens between theanodes, which screens extend to the cathode screen. These tubes,however. are only suitable for eiective anode voltages of severalhundreds of volts, since the screens do not prevent ions from wanderingdirectly from one anode to the other. At low voltages this is generallynot very troublesome, since almost all ions reach the cathode where theyare neutralized, but at higher voltages the ions often pass directlyfrom one anode space to the other.

In regard to voltages exceeding several hundreds of volts, rectifyingtubes having a plurality of anodes were hitherto often designed as acylindrical or spherical glass bulb wherein the cathode was provided, ifrequired within a cathode screen. whereas the -anodes were fitted in acorresponding number of anode arms of the bulb having a great length andbeing once or several times curved. As a result of the long curved armsany ions wandering to one of the anodes are collected by the wall of theanode arm so that the ion bombardment on the anode remains small.However, the arms also collect many ions in the positive phase so thatthe arc voltage and consequently the losses become high. Sometimes itlis necessary to provide auxiliary electrodes in the arms or to equip thearms on the outside with a conductive layer to prevent the ignitionvoltage from becoming too high. In addition the arms require much spaceand render the tube breakable and expensive.

Furthermore it is known to house the incandescent cathode of a tubehaving two anodes within a screen and to divide this screen, by means ofa screen placed at the middle, into two parts each of which cooperateswith one anode.

25 By placing the screen at the middle of the cathode it is to beensured that the ions cannot find their way. through the cathode space,from one discharge path to the other. In this case. there areconsequently two different cathodes as it were that are not in the samefavourable load l lets must be provided.

The present invention has for its object to prevent these disadvantagesand drawbacks in a rectifying tube having two or more anodes. in whichthe incandescent cathode is housed within a cathode screen, by choosingthe distance d from any anode to the cathode screen in such a mannerthat a correct product of this distance and the pressure in the tube issmaller than the value at the minimum of the Paschencurve for thefilling in question of the tube, the cathode screen and. it required,other screens being fitted in the tube in such a manner that asaaaistheir way from the space for one anode to the space for another anode.Consequently, the charge carriers in the space for one anode can reachthe cathode space only where they are collected and neutralized by thecathode. With the same power'. tubes designed according to the inventionhave a much smaller circumference than tubes having arms. I

In a particularly suitable construction the spaces in front of theanodes communicate only through long. narrow and preferably curvedslits,

' the cathode screen' being usually closely surrounded by the wall ofthe tube. As a result ofthe narrow slits charge carriers are not able tomove freely from one anode space to mother, since they are 'sooncollected by the walls thereof.

In tubes for very high voltages it is advantageous to cover theapertures for the passage of the discharge `by means of little screenspreferably housed in the cathode screen. The screens covering theapertures for the discharge prevent ions from entering the cathodescreen at a high velocity, 'due to which they would fly pest the cathodeand reach any of the other anodes through one of the other apertures.Moreover. the screens have the advantage of preventing activatingmaterial disintegrating from the cathode from finding its way to theanode.

In a suitable form of construction of a tube according to the inventionthe anodes are mounted symmetrically. The temperature and consequentlythe arc voltage of each discharge path is the same during operation ofthe tube, so that uneven arc voltages do not cause additional higherharmonics in the rectified current.

In another suitable form of construction the anodes are closelysurrounded by the glass wall and the front surface of the anodes isadapted to the form of the cathode screen, the diameter of the frontsurface of the anodes at least amounting to four times both the distanced from the anodes to this screen and the diameter of the dischargeapertures in the cathode screen, and the product pd of the pressure inmillimeters of the gas in the tube times the distance in centimetersfrom the anode to the screen being between 0.00015 and 0.015. In thisconstruction the distance from the anodes to the cathode screen ispractically constant, and as a result of the anodes being closelysurrounded by the glass wall and of the small size of the dischargeapertures and the distance from the cathode screen to the anodes incomparison with the diameter of the anodes it is achieved thatpractically no charge carriers are able tol gain access to the back of:

the anodes, so that the tube is free from arcing back even at very highvoltages.

In order that the temperature of the anodes and the surrounding glasswall may be kept low, in spite of the compact construction of the tubesaccording to the invention, the following form of construction offersespecial advantages. In

y this form the anodes, which are designed as cylindrical boxes closedon one side. are sealed with the open edge to the glass wall, so thatthe outer side of the anodes is cooled by conduction and convection, forinstance exclusively by natural circulation of the air or by forcedcooling, thereby cooling the inner anode surfaces. Though the screensfor covering the discharge apertures may be directly connected to thecathode screen or. as an alternative. may be so provided as to beinsulated therefrom without being connected to a definite voltage, it isespecially advantageous to apply s positive voltage to these screens,for which either a constant direct voltage or s pulsating direct voltagemay be made use of. In fact. since the screens have a positive voltagethey prevent, even under the worst conditions, posi- 'tive ions frombeing drawn to an anode having a negative potential, and this becausethe screens repel the ions. In the positive phase they have theadvantage of operating as a grid facilitating the first ignition of thetube. Similarly to all grids in gas-nlled tuba the screens ako act to sgreater or less degree as an auxiliary snode by htlh the ignition of themain current is facili- In order that the invention may be more clearlyunderstood and lreadily carried into eect it will now be described withreference to the accompanying drawing. wherein Figures 1 and 2 are avertical and a horizontal section respectively of a tube according tothe invention, in which the symmetrically mounted anodes are sealed tothe wall of the tube. Figure 3 representing a tube according to theinvention. in which the discharge apertures in the cathode screen arecovered by distinct screens, and Fig. 4 is a sketch of the so-calledPaschen curve.

In Figures 1 and 2 the reference member I denotes the glass wall of thetube. The cathode 2 is provided within the cathode screen I3 which isclosely surrounded by the wall I. Three anodes are placed at a shortdistance from the cathode screen and consist of hollow chrome iron boxes4 each having a layer of carbonized iron Il as an active surface. Eachanode is equipped with a connecting terminal 1. The cathode is securedto the terminal wires s which 1nA their tum ire .secured to the chromeiron hoods I welded t`o the tube. The cathode screen is secured to theterminal wires l by means of the clips l and the insulating rings i. Thecathode screen 3 is furnished with a supply wire il leading to anoutlet. The stock of mercury I2 is contained in the chrome iron cap ii.The anodes are sealed with the open back Il to the glas of the tube. Asa result thereof the metal of the anodes directiy contacts the open airso that the temperature is very low. In front of each anode the cathodescreen is furnished with an aperture I3 for the passage of thedischarge. Any ions penetrating inside the cathode screen are collectedand neutralized by the cathode. There is substantially no penetration bythe anode field. into' the cathode screen through the apertures i3 sothat along this path substantially no ions can find their way from thespace for one anode to the space for another anode. To prevent chargecarriers from moving directly from one anode to the other the cathodescreen is equipped with three circular metal screens i1 embracing anedge of the similarly shaped glass rings II. It is practicallyimpossible for charge carriers to pass through the narrow slits 8abetween rings II and I1, so that a breakdown between two anodes is notpossible also along this path.

In Figure 3 parts corresponding to those of Figures l and 2 bear thesame reference numerals.-

The apertures i3 are covered by screens Il which are insulated from thecathode screen and each of which has a separate outlet. For thedischarge m each anode a comparatively narrow annular slit is left. Ionscoming from one of the anodes at a high velocity are collected by thecathode screen 3 or one of the screens i8. Any ions penetrating into thecathode screen generally have a low velocity only, so that they arereadily neutralized by the cathode. `As clearly appears from the drawingnot only the cathode screen is closely surrounded by the glass wall, butalso the upright side of the anodes. Consequently discharges cannotoccur at the back of the anode. The front surface of the anodes providedat the sides of the tube has a curvature in a plane normal to the planeof the drawing, in such a manner that the distance between the frontsurface and the cathode screen has a substantially constant value. Thestock of mercury I2 is provided in a bulb I9 into which reach thegauge-covered ends 20 of the sealed exhaustion tubulation. The tube,whose size is about 1%; times as large as that of the tube shown in thedrawing, accommodates an effective alternating anode voltage of 10 kv.and a current of 2.5 ampper anode i. e. the tube is capable ofrectifying a power of 75 kw. In this tube the screens I8 receive apositive voltage of to 20.

In Fig. 4 is illustrated a typical Paschen curve substantially as itappears when plotted on a double logarithm scale. Various Paschen curvesare published in Nederlandsch Tijdschrift voor Natuurkunde (NetherlandsJournal for Physics) in the article by F. M. Penning entitled HetVerband Tusschen de Doorslagkromme van Paschen en de ElementaireProcessen, vol. 5, pages 146-151 (see Figure 3 of the article). Such acurve specifically prepared for mercury, for example, may be found inthe article by F. Llewellyn Jones and W. R. Galloway in Proc. Phys. Soc.London, 1938, vol. 50, page 27, especially in Fig. 2 on page 210. It ispreferable that the product p X d, where p is the pressure in the tubeand d is the distance of separation between any anode surface and theopposed cathode screen surface be less than the minimum point on thePaschen curve.

What I claim is:

1. A gas filled rectifying tube comprising an envelope, a cathode withinsaid envelope, a catlrr ode screen within the envelope and surroundingsaid cathode, a plurality of anodes having active surfaces substantiallyparallel to and facing surfaces of said screen on the side of the screenremote from said cathode, said screen having screen apertures interposedbetween said cathode and each said anode, said envelope and said screendening anode chambers communicating with each other through elongatednarrow passageways.

2. A gas filled rectifying tube comprising an envelope, a cathode withinsaid envelope, a cathode screen within the envelope and surrounding saidcathode, a plurality of anodes having active surfaces substantiallyparallel to and facing surfacesof said screen on the side of the screenremote from said cathode, the product of the gas pressure p and thedistance d of separation between said anode and screen surfaces beingless than the minimum point on the Paschen curve for the gas filling ofthe tube, said screen having screen apertures interposed between saidcathode and each said anode, said envelope and said screen defininganode chambers communicating with each other through elongated narrowpassageways.

3. A gas filled rectifying tube comprising an envelope, a cathode withinsaid envelope, a cathode screen within the envelope and surrounding saidcathode, a plurality of anodes having active surfaces substantiallyparallel to and facing surfaces of said screen on the side of the screenremote from said cathode, said screen having screen apertures interposedbetween said cathode and each said anode, said envelope and said screendefining anode chambers communicating with each other through elongatednarrow passageways, and individual screen members interposed betweensaid screen apertures and said cathode.

4. A gas filled rectifying tube comprising an envelope. a cathode withinsaid envelope, a cathode screen surrounding said cathode, said envelopeand said screen defining a plurality of anode chambers, a plurality ofanodes symmetrically arranged about said cathode in said chambers andseparated from said cathode by said screen, said screen having screenapertures interposed between said cathode and each said anode, saidanode chambers communicating with each other through elongated narrowpassageways, and individual screen members interposed between each ofsaid screen apertures and said cathode.

5. A gas lled rectifying tube comprising an envelope, a cathode withinsaid envelope, a cathode screen within said envelope and surroundingsaid cathode, said screen and said envelope defining a plurality ofanode chambers, an anode in each of said chambers each having activesurfaces substantially parallel to and facing surfaces of said screen onthe side of said screen remote from said cathode, said screen havingscreen apertures interposed between said cathode and each said anode,said anode chambers communicating with each other through elongatednarrow curved passageways, and individual screen members interposedbetween said screen apertures and said cathode.

MINNE KUIPERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

